1. Field of the Invention
The invention relates to protection against fires and more particularly to an installation for detecting fires in the very first stage of development, by the use of micro-containers containing a gaseous fluid which is released by the bursting of the micro-containers when the temperature in the vicinity of these micro-containers reaches a predetermined value.
2. Description of the Prior Art
Conventional fire detecting processes operating by reaction to the heat, smoke, combustion gases or the flames can only intervene when the combustion is sufficiently advanced to produce in the region of the detector a sufficient amount of heat to enable the latter to react, outside normal fluctuation conditions. Depending on the type, the heat excites the detector either directly or by the conveyance of the products of combustion by a rising effect so as to cause them to enter the detector, or this heat brings to a high temperature a body which produces, for example, electromagnetic, infrared or ultraviolet radiations to which the detector is responsive.
All these detecting processes have a major drawback which resides in the fact that the fire can only be detected at a stage of development at which it is already dangerous or its subsequent development is extremely rapid, since, in practice, the detecting devices can only react at the moment at which flames have already developed.
Consequently, it has been attempted to obtain an earlier detection of fires and this is why it has already been proposed (see DAS No. 1 149 277) to employ small explosive cartridges (Knallscheiben) which are for example incorporated in the coat of paint covering the walls of the enclosure to be supervised. However, in this case, the composition of these cartridges, which is purely and simply an explosive, increases the fire rather than tends to put it out, and it is therefore dangerous to proceed in this way, from the point of view of both the fire and persons, above all when there is a danger of explosion in the protected space owing to the nature of the objects therein (chemical or other installations). Further, the DAS No. 1 149 277 is completely silent on the conception of an installation for detecting the noise of the explosions and using this detection of noise, at the right time, for setting off the alarm. Recently, there has been used a new process employing micro-containers containing an extinguishing product, the micro-containers being made from a material which is capable of deteriorating under the effect of a predetermined temperature and thereby releasing the extinguishing product. (See in particular the Dutch application No. 77 13 309 of Dec. 1, 1977 to Anthonius Hermanus Pietersen). The extinguishing product contained in the micro-containers is a gas having a high expansion power such as, for example, bromo-fluoro-alkane which may be CF.sub.3 Br in a preferred embodiment. Such a gas has the property of extinguishing and retarding the fire.
The use of these micro-containers has the advantage of permitting the fighting of the initial stage of the fire in the precise region where an abnormal rise in the temperature occurs. Indeed, by their very nature (their diameter is, for example, between 200 and 260 .mu.m), the micro-containers may be incorporated, for example, in coatings such as paints, furnishing fabrics or the like, or provided in objects having an outer layer of plastics material such as, for example, electric cables.
Up to the present time, it has been proposed to use only the fire extinguishing or retarding property of the gases contained in the micro-containers, which burst under the effect of the temperature. However, under these conditions, it is not possible to rapidly ascertain that the micro-containers have burst in an enclosure to be supervised, so that the personnel in charge of the supervision is only informed of the start of a fire when the detectors of conventional type mentioned hereinbefore have had time to set off an alarm. In other words, the early detection in fact effected by the micro-containers in the precise region of the start of the fire is not utilized.
It is known, from French Pat. No. 1 375 077, to protect a premises against theft by a detection of disturbances or vibrations produced at the moment of breaking in, by means of vibration transducers and to provide a circuit capable of distinguishing the significant vibrations of the breaking in from surrounding vibrations which are always present. However, this circuit, which operates essentially by a filtering of frequency followed by an integration, is not appropriate, owing to the essentially analog nature of the processing of the detected signal and owing to the signal itself, for processing the noise of the bursting of micro-containers which is mainly of a digital nature since it is formed by a series of noise pulses.